Acetylene is widely used in oxy-acetylene torches by means of which temperatures of up to 3500.degree. C. can be reached for welding and cutting of metals. Acetylene, however, is inherently unstable and, at pressures greater than about 2 atmospheres, may explode violently.
Under current industrial practice, acetylene is safely stored and shipped in steel cylinders under a pressure of about 15 atmospheres. The acetylene-containing cylinders are produced by filling the cylinder with a porous material and injecting into the cylinder a solvent, usually acetone, in which acetylene is soluble. The porous material comprises a capillary system of interconnecting micropores, typically having a size range of about 10 to 20 microns, and is typically calcium silicate having a porosity in excess of 90%. Acetylene is then introduced into the cylinder and is distributed throughout the capillary system of the porous material as a result of dissolution in the acetone. In this way, it is possible to ensure safe storage of dissolved acetylene in quantities of up to eight times the volume of the gas which could be stored without the porous mass/solvent system.
During the lifetime of acetylene cylinders, they are subjected to numerous gas filling, gas discharging and transportation operations. During any of those operations, the cylinder can be subjected to corrosive chemicals, dents, gouges, fire, arc burns and other damaging events such as breakdown of the internal porous mass. As a result of such damaging occurrences, the cylinders are often rendered unfit for subsequent use and must therefore be disposed of in a safe manner.
Exhausted acetylene cylinders containing residual acetone which could otherwise leach into the environment upon disposal of the cylinder are classified as a hazardous waste under the environmental protection laws. Moreover, on-site storage of a hazardous waste also constitutes a violation of the environmental protection laws. In addition, acetone is expensive and gives rise to increased costs if not recovered from exhausted acetylene cylinders.
Thus, a need exists to develop an effective way of removing residual acetone from exhausted acetylene cylinders to thereby convert the cylinders from a hazardous waste to an acceptable solid waste, and also to enable recovery of acetone for further use.